The present invention relates to the removal of aerobic pollutants from the ground and, in particular, to a method and apparatus for removing such aerobic pollutants by oxygenating the ground water.
Hydrocarbon spills, such as oil, gasoline and the like, are toxic wastes which damage the environment by permeating the ground into which they are spilled. The existence of hydrocarbon toxic wastes on a parcel of real estate can prevent the owner from obtaining building permits leading to development, lead to the shut down of existing activities carried out on the parcel and render the parcel unmarketable. One method of removing hydrocarbon pollutants from the ground is to encourage the growth of bacteria within the ground that feed on the toxic hydrocarbon molecules to convert them into non-toxic waste products. Another method is to oxygenate the ground to thereby encourage the oxygenation of the toxic hydrocarbon molecules to thereby convert them into non-toxic molecules.
Soil contamination typically arises from leakage from oil and fuel tanks, and the associated piping and the process of filling and emptying such tanks. Hydrocarbons contaminate unsaturated soil by the forces of gravity and the movement of surface water which cause the contaminants to spread over an area much greater than occupied by the tanks alone. Over time, the petroleum products will leach into the underlying ground, spreading horizontally and downward through the pores in the soil. Upon reaching the ground water, the petroleum will pool and move with the ground water to contaminate adjacent ground.
The primary pollutants from gasoline and the like are benzene, toleune, ethylbenzene, xylene (BTEX) and methyl-tertiary-butyl-ether (MTBE).
A number of methods are currently available for reclaiming polluted ground. One method is to remove the contaminated soil to a secure site. Another is to treat the ground with physical, chemical or biological means. A third is to withdraw existing ground water and treat the water with chemicals or biological organisms and return the water to the ground. Generally, in-situ treatment of the water in the ground is the slowest and least expensive technique for recovering contaminated ground.
An obstacle to in-situ biological techniques for recovering contaminated ground has been supplying enough oxygen within the ground to encourage the chemical reactions needed to bring about the degradation of pollutants into non-toxic chemicals. Efforts have been made to force air into the ground, or to apply pure oxygen or oxygen-releasing chemicals into a contaminated area. Where the delivery of such oxygen is low compared to the amount of toxins in the contaminated ground, the clean up time can be prolonged. Also, existing methods of oxygenating ground are expensive and not always effective. For example, delivering gas or oil into the ground under too high a pressure will result in the formation of escape pathways which reduce the efficiency of the oxygen being applied to the ground.
In accordance with the present invention, the oxygen in contaminated ground is increased by the oxygenation of the ground water. To oxygenate the ground water of a parcel of contaminated ground, a plurality of vertical wells are drilled into the ground, the wells being spaced sufficiently close to one another to oxygenate the intervening ground. Preferably, twenty to twenty-five feet should separate adjacent wells. Each well must extend below the water table and the deeper the well extends below the water table, the greater the area surrounding the well that can be oxygenated.
To oxygenate each well, an oxygenation unit is lowered therein. The oxygenation unit consists of a length of tubing having an upper and lower end with a tubular wall extending between them. Within the tubing is a plurality of parallel electrically conductive plates extending parallel to each other and parallel to the axis of the tubing. The plates are spaced from one another and an electrical potential is applied across adjacent plates such that electrolysis will break down water between the plates into the chemical components of O2 and H2. Water in the wells moves across the plates by means of a pump thereby allowing the water to absorb the O2.
In the preferred embodiment, an air flow draft pump is provided, consisting of an inverted funnel having a frustoconical portion with a large diameter lower end positioned immediately above the plates and a small diameter upper end positioned a short distance above the large diameter lower end and a vertical tube extending from the small diameter upper end. An above ground air compressor directs pressurized air through a flexible tubing which extends down the well and into the oxygenation unit with the distal end extending through the wall of the funnel with an outlet immediately above the plates.
Preferably, between five and twelve volts are applied across the plates to generate a current of between one and one half and four amps. The tube for the oxygenation unit is preferably positioned at the upper end of the well at least three feet below the ground water level for oxygenating an area of ground having a diameter of approximately six feet from the well. To oxygenate an area of fifteen to twenty feet from the well, the oxygenation unit should be positioned at least ten feet below the ground water level. The forced air from the pump is released above the plates and moves up through the tube at the upper end of the funnel and draws water with it, creating a draft to pull new water from adjacent ground into the well below.
The bubbles of air which are released at the upper end of the funnel tube create a frothing of water which rises above the level of the ground water. The greater the amount of compressed air pumped into the funnel, the higher the froth of water will rise above the ground water level thereby cresting a head of water extending higher than the existing water table. A perforated tubing is used to define the walls of the well and the froth of water which extends above the ground water level overflows into adjacent ground water and spills outward of the well in the form of an underground wave.
As a result of the injection of oxygen into the water of oxygen formed on the plates, the frothing water flowing into adjacent ground has an oxygen level of about twenty parts per million (ppm) which is sufficiently high to cause the degradation of hydrocarbons into non-toxic chemicals. As the water continues to flow outward, it settles downward into the ground water and gradually increases the oxygenation of the ground water surrounding the well. As the water moves away from the upper end of the well, the level of oxygen in the water falls off. After a period of time the distribution of oxygen between adjacent wells elevates and finally reaches a stable equilibrium. Where the oxygenation unit is positioned at least ten feet below the water level, the water within fifteen to twenty feet from the well will reach an oxygen concentration of one ppm within about ninety days after the oxygenation unit has been put into operation. The one ppm concentration of oxygen in the ground water is sufficient to support the growth of bacteria needed to needed to detoxify the ground. Hydroxyl radicals (2OH)xe2x80x94are strong oxidizer which contributes to the breakdown of toxic chemicals.
To control other contaminants, such as chlorine producting salts, a sock filled with activated carbon or an ion exchange material can be positioned within the tubing below the plates.
It should be appreciated that although it has been well known that oxygen in the ground water would stimulate bacteria, to the applicant""s knowledge there have been no prior efforts to use hydrolysis to oxygenate ground water because all laboratory models have produced high levels of free chlorine which in turn inhibits bacteria growth. I have found that although significant amounts of free chlorine are formed, the chlorine does not significantly interfere with the bacterial growth. The applicant presumes this is because the chlorine weighs about one and a half times the weight of water and because the chlorine quickly combines with other substances. The chlorine actually provides a benefit because it prevents bacteria from forming in the immediate vacinity of the oxygenation units.